The invention relates to a starter-generator for a motor vehicle, having an electrical machine that can be coupled selectively to an internal combustion engine and/or a transmission of the motor vehicle. Known starter-generators of this kind are attached to the drive train of a motor vehicle via a belt drive or cone wheels. Both types of attachment mean that the starter-generator is laterally offset relative to a structural unit comprising the engine and the transmission, which makes it difficult to combine the starter-generator with the above two components to make a compact, space-saving component group.
The starter-generator of claim 1 makes it possible to create a compact structural unit, because with the aid of the starter-generator according to the invention as an intermediate element, the engine and transmission can be combined linearly into a unit.
With this kind of tightly packed arrangement, efficient cooling of the electrical machine of the starter-generator is important. It is therefore also proposed that a cooling conduit extends, swinging axially back and forth, in a radial outer wall of the housing be provided. This course of the cooling conduit not only makes it possible to make the cooling conduit longer than the circumference of the housing but also makes it possible, as means for securing the starter-generator to the engine or transmission housing, to provide blind bores for screws, bolts or the like, which each extend from one face end into the outer wall of the housing, at a point where the cooling conduit extends at a distance from the applicable face end. Thus despite the presence of the cooling conduit, the entire thickness of the radial outer wall is available for securing the starter-generator to the engine or the transmission housing. The housing of the starter-generator is preferably produced in one piece in a casting process. A casting core required for forming the cooling conduit, for example comprising molding sand, can be removed after the casting is done through slots on one of the end faces of the housing. These slots are expediently tightly closed after the casting core has been removed.
Alternatively, a casting core, for example comprising a plastic foam, that evaporates in the casting can be used. In such a case, it is possible to dissipate the resultant vapor via coolant connections of the cooling conduit that have to be provided anyway. Under these conditions, the aforementioned slots can be omitted.
The rotor of the electrical machine is expediently supported by a radially extending flange that is part of the housing. Between the flange and the rotor, an actuator can be provided, which acts as a final control element for actuating a coupling for the starter-generator.
A hollow chamber is formed on the side of the rotor toward the flange, which offers space for a pulse wheel and a sensor for detecting a rotation. To enable rotation of the rotor with the closest possible tolerances and consequently the smallest possible air gap between the rotor and an associated stator, the rotor is supported via roller bearings, that is, in particular via one or two ball or needle bearings.
In a preferred embodiment, the rotor includes a lamination packet with short-circuit rings and short-circuit bars as well as armoring rings, which are anchored on the ends of the short-circuit bars that protrude from the axial face ends of the lamination packet. By the provision of the armoring rings on the axial end faces, a weakening of the material comprising the short-circuit rings and short-circuit bars or the lamination packet, or an enlargement of the air gap, which would be necessary if the armoring rings were attached radially on the outside, is avoided. Nevertheless, the armoring rings offer effective protection of thexe2x80x94preferably copperxe2x80x94short-circuit bars against centrifugal force, and in particular they prevent the protruding ends of the short-circuit bars from flowing radially outward.
Additional functions of the armoring rings can be axially fixing the rotor to its hub or balancing the rotor. Selectively removing material from the armoring rings, especially from the radial inner side, makes exact balancing of the rotor possible without this having any effect on the mechanical stability or electrical properties of the rotor.
According to another preferred embodiment, the rotor includes a lamination packet with short-circuit conductors, and the short-circuit conductors are formed by lining recesses of the lamination packet, for instance by means of die-casting of aluminum. Since the material strength in this kind of rotor construction is greater than if copper short- circuit bars and short-circuit rings are used, the armoring rings can be omitted, which simplifies production and lowers assembly costs.
To make it possible for the axial structural length of the starter-generator to be kept as short as possible, it can be provided that the winding heads of the stator of the electrical machine are bent in the radial direction.
A stator of the electrical machine is preferably thermally joined to the housing. In this way, by simple means, a large-area thermal contact with considerable contact pressure and accordingly good heat transfer properties can be created between the stator and the housing.